Presentation
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Bilateral human laryngeal motor cortex in perceptual decision of lexical tone and voicing of consonant
Poster A84 in Poster Session A, Tuesday, October 24, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Also presenting in Lightning Talks A, Tuesday, October 24, 10:00 - 10:15 am CEST, Auditorium
Yi Du1,2,3,4, Baishen Liang1,2, Yanchang Li1, Wanying Zhao1; 1Institute of Psychology, Chinese Academy of Sciences, 2Department of Psychology, University of Chinese Academy of Sciences, 3CAS Center for Excellence in Brain Science and Intelligence Technology, 4Chinese Institute for Brain Research
Introduction: Recent neuroanatomical models propose that the left motor cortex maps phonological analyses onto motoric representations, which may compensate for degraded speech perception in challenging listening conditions. Transcranial magnetic stimulation (TMS) studies have identified a causal engagement of the left lip and tongue motor subregions in phoneme perception, while the right motor cortex has been linked to perception of non-lexical prosody. However, three questions regarding the role of bilateral motor cortices in speech perception remain unanswered: 1) whether the laryngeal motor cortex (LMC) is engaged in an effector-specific manner, 2) how bilateral motor cortices cooperate under varying degree of difficulty, and 3) what specific stages of the perceptual decision-making process are modulated by bilateral motor cortices. Four hypotheses targeting the first and second questions (spatial questions) may drive the functional distributions of bilateral motor cortices: the acoustic hypothesis (the left motor cortex for segmental and the right for suprasegmental cues as auditory cortices), the lexical hypothesis (the left motor cortex for lexical cues), the motor hypothesis (bilateral motor cortices show somatotopy during perception resembling production), and the redundancy hypothesis (the left motor cortex is fundamental and the right acts as a backup). For the third (temporal) question, as speech perceptual decision is postulated to encompass the (left) motor cortex in acoustic-phonetic feature extraction, phonemic categorical mapping and response selection, we hypothesized that bilateral motor cortices may interactively involved in all the stages. Methods: To test the hypotheses, we delivered repetitive TMS (rTMS, Experiment 1, an exploratory experiment) or theta-burst stimulation (TBS, Experiment 2) to the left/right motor cortex (in Experiment 1, LMC and tongue motor cortex, TMC; in Experiment 2, LMC only) of Mandarin speakers to investigate if the categorical perceptual decision of lexical tone (a suprasegmental lexical cue determined by laryngeal gestures) and dental plosive consonant (a segmental lexical cue determined by both laryngeal voicing and tongue motions) with/without noisy background would be modulated accordingly. To localize the production-related dorsal LMC (dLMC) and TMC, participants underwent a functional magnetic resonance (fMRI) pretest where they performed phonation and tongue movement tasks. We applied two independent pipelines to investigate the TBS modulation effects upon dLMC on behavioral responses in Experiment 2. For perceptual sensitivity, we fitted psychometric curves to investigate modulations on the curve slope. For stages of perceptual decision, we applied the hierarchical Bayesian estimation of the drift-diffusion model (HDDM) to disentangle what latent dynamic decision processes would be altered. Results: Our results reveal an effector-specific involvement of bilateral dLMCs in perceptual decision of both lexical tone and voicing of dental plosive consonant, supporting the motor hypothesis. Meanwhile, we provide evidence for the redundancy hypothesis, as the left dLMC plays a dominant role, while the right counterpart is only crucial in challenging tasks. Moreover, the specific perceptual decision stages that are modulated by the dLMC hinge on the hemisphere and task difficulty. Conclusion: Taken together, these findings expand our knowledge of the underlying mechanisms and temporal dynamics of bilateral motor engagement in speech perceptual decision-making.
Topic Areas: Speech Perception, Multisensory or Sensorimotor Integration